The present invention relates to a method and apparatus for making filter mouthpieces or filter plugs, and more particularly to improvements in a method and in a machine for the production of filter rod sections which can be used in filter tipping or analogous machines for mass-production of filter cigarettes, cigars or cigarillos.
Filter rod sections are obtained by subdividing a continuous filter rod which normally contains a rod-like filler of fibrous filter material and a tubular envelope consisting of cigarette paper, imitation cork or other flexible wrapping material draped around the filler. The filler is formed by advancing a so-called tow of filamentary filter material (e.g., acetate fibers) through several processing stations, such as one or more banding stations where the normally crimped filaments are separated (disentangled) from one another, a stretching station where the filaments are stretched to reduce, eliminate or uniformize the crimp, a spreading station where the filaments are spread apart to form a thin layer, a station where the filaments of the layer are contacted by a finely atomized liquid plasticizer, and a gathering station where the layer is converted into a rod-like cylindrical body or filler. Such filler is thereupon draped into a web of cigarette paper or the like, and the resulting continuous filter rod is severed by a suitable cutoff to yield a succession of discrete filter rod sections of desired length, e.g., six or eight times unit length.
As a rule, the tow is supplied in the form of a bale wherein the tow is looped back and forth and is condensed so that the bulk of the bale is reduced to a minimum without unduly affecting the quality of the filamentary filter material. In order to avoid the need for a stoppage of the filter rod making machine when a supply (bale) of running tow is exhausted, the trailing end of the running tow is normally spliced to the leader of the next-following (fresh) tow so that the making of the filler can proceed without interruptions. This is highly desirable because the threading of the leader of a fresh tow through the filter rod making machine is a time-consuming operation, i.e., each such threading entails substantial losses in output, especially in a modern filter rod maker which can turn out many thousands of filter plugs per minute. The splice between two successive tows is formed by welding or by otherwise bonding the trailing end of the running tow to the leader of the fresh tow. To this end, the trailing end is placed over the leader or vice versa, i.e., the thickness of the splice exceeds the thickness of a single tow. Moreover, such splice constitutes a non-homogeneous portion of the composite tow, i.e., the characteristics of filter plugs which contain portions of a splice deviate from the characteristics of other (acceptable) filter plugs so that it is highly desirable to segregate from a production line (including, for example, one or more filter rod making machines, one or more cigarette rod making machines, one or more filter tipping machines and one or more packing machines) all such filter rod sections which contain portions of or entire splices. As a rule, the density of the filler in a filter rod section which contains a portion of or an entire splice is likely to be higher than desirable since the cross-section of the splice must be reduced to the cross-section of the filler which is obtained from a running tow. Moreover, welding of the leader of the next-following tow to the trailing end or portion of the preceding (expired or expiring) tow is likely to result in hardening of the respective portion of the filler so that it might affect the integrity of the envelope, for example, by causing the seam between the overlapping marginal portions of the web of wrapping material to open. This means that the corresponding filter cigarettes, cigars or cigarillos must be segregated from satisfactory smokers' products with attendant losses in tobacco.
The formation of a splice which is, or which is likely to be, harder than the normal filler of a filter rod can cause other problems in a modern high-speed filter rod making machine. Thus, the width of various clearances (such as gaps between the elements of so-called tow banding devices, the width of nips of advancing, stretching and spreading rolls for the tow, and the width of the passage at the plasticizer applying station) is normally selected with a view to ensure the making of an optimum filler from a tow of normal thickness and hardness, i.e., the width of such clearances may not suffice to allow for unimpeded passage of a splice. The situation is aggravated in a modern filter rod maker wherein the tow is transported at a high or extremely high speed in order to ensure that the filter rod making machine can meet the requirements of a modern high-speed filter tipping or like machine. Therefore, a splice is likely to be caught in the banding, spreading, stretching and/or plasticizer-applying unit or units of the machine, and this can lead to damage to component parts of the machine and/or to breaking or tearing of the tow with attendant losses in output which are occasioned by the need to thread the leader of the tow behind the break through the filter rod making machine.
In accordance with heretofore known proposals, the speed of the filter rod making machine is reduced whenever a splice is about to be transported therethrough. This is less likely to result in breakage of the tow because the splice can pass more readily through the afore-enumerated stations if its speed is less than the nominal or normal operating speed. The speed of the prime mover is reduced by hand, and the attendant observes the progress of the splice through the machine so that the speed of the prime mover can be increased back to normal as quickly as possible after the splice has been advanced through the machine. However, even though such mode of manipulating the machine reduces the likelihood of breakage of the web, it does not prevent the defective or less satisfactory filter rod sections (namely, those sections which contain the splices or portions of the splices) from reaching the next machine or machines of the production line, i.e., such filter rod sections will contribute to the making of defective smokers' products. If not detected, the defective smokers' products will constitute an annoyance to the purchaser. Alternatively, such defective filter rod sections must be detected by resort to complex and sensitive testing equipment so as to prevent their entry into the next machine, such as a filter tipping machine.